The present invention relates to a method for separating and or concentrating cobalt and nickel and the like from alloys which can be advantageously applied to volume-reducing and decontamination of solid waste from nuclear power plants, separation of cobalt, nickel and the like from manganese nodules and from suitable iron alloys.
In general, it has been considered technically difficult to separate iron group metals such as cobalt, nickel and the like from iron alloys pyrometallurgically.
However, such technical method for separating cobalt, nickel and the like from iron alloys is very important, for instance, in decommissioning or dismantling and removing nuclear power plants having noninflamable solid waste to be processed, for separating or concentrating cobalt, nickel and the like from manganese nodules or in concentrating iron alloys.
For instance, the noninflamable waste from the nuclear power plant includes air-conditioning filters, heat-insulating materials, various kinds of metals, concrete and so on. Such nonflammable waste materials are stored in cans. In the case of a boiling water reactor with a capacity of 1100 MW, the waste materials mount to about 500 cans a year. Such noninflamable materials are less in quantity than other waste so that they are stored without being subjecting to volume reduction processes, but it is quite apparent that some countermeasures must be taken in the future when the noninflamable materials are increasedly accumulated. Meanwhile, methods for decommissioning and removing a terminated nuclear power plant have been studied. In decommissioning and removing an old nuclear power plant, a great quantity of noninflamable materials must be handled so that methods for reducing their volumes have intensively studied. With respect to volume reduction of noninflamable waste materials, it is also very important to develop a method for removing radioactive materials mixed with and attached to the waste materials; that is, a decontamination method. Furthermore it is preferable to recover nonradioactive metals effectively.
In nuclear power plants, corrosion products are irradiated with neutrons in the core and become radioactivated. Such radioactive materials are entrained in cooling water and accumulate on inner surfaces of various devices and equipment of the nuclear power plants. In this case, nuclear species contribute the strength of radiation as shown in FIGS. 1(A) and 1(B). FIG. 1(A) shows radioactive decay of inner wall surfaces contaminated with sediment in boiling water reactor (BWR) and FIG. 1(B), radioactive decay of radioactive corrosion products in pressurized water reactor (PWR). It is seen from these graphs that in both of BWR and PWR, their devices and equipment are contaminated mainly with .sup.60 Co.
There has not yet been proposed a satisfactory method for separating the iron group metals such as .sup.60 Co attached to and mixed with carbon steel and stainless steel since Fe and Co are in the same group in the periodic table and are quite similar physically and chemically.
Meanwhile, in order to recover valuable metals such as Co and Ni from manganese nodules, research and development of hydrometallurgical refining processes such as cuprion-ammonia leaching process and high-temperature high-pressure sulfuric-acid leaching process has been made. The hydrometallurgical refining processes can be carried out at relatively low temperatures so that they can be said to be energy-saving processes, but they have the problems that large quantities of chemical agents and water are needed and that a large area is needed. Furthermore, there are problems of how to transport low-quality minerals such as manganese nodules, garnierite or tetrite and how to dispose large quantities of waste after refining. Therefore there has not yet been proposed an effective preliminary process for concentrating valuable metals from such low-quality minerals.
In view of the above, the present invention has its object to provide a method for separating iron alloys having extremely low concentrations of cobalt and nickel and to provide iron alloys having a high concentration of cobalt and nickel by utilizing a kind of the pyrometallurgical solvent extraction processes. Another object of the present invention is to provide effective separation of radioactive cobalt from iron alloys of solid waste materials discharged from nuclear power plants, thereby obtaining Fe Co alloys having an extremely low concentration of .sup.60 Co, and to provide remarkable reduction of the volume of concentrated Fe..sup.60 Co alloys. The present invention has a further object for subjecting low-quality minerals such as manganese nodules and scraps to a pyrometallugical process so that the quantities of chemical agents and water needed for wet refining of cobalt and nickel can be decreased.
The above and other objects, effects and features of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.